Screen grid tube



Feb. 24, 1942. J. E. 85665 SCREEN (mm was Filed June 16, 193B 2 Sheets-Sheet 1 i cn f lim PLATE GUC/FET TERMINAL com/r04 cur/0 soc/r57- HEM/1m Inventor: James E. B6225, b x m alml y His Attorney.

Patented Feb. 24, 1942 SCREEN can) TUBE JamesE- 'Bc gs; Schenectady, N. -Y., assignor' to General Electric' y, a corporation of New York Application June 16, 1938, Serial No. 214,104

'6- Claims.

The present invention relates to electric discharge devices and more particularly to glass and-metal radio tubes.

In the design and manufacture'of radio tubes and particularly for convenience in mounting these tubes on the chassis and making connections to the electrodes, it may bedesirableunder certain circumstances to bring out all of the leadingin conductors from one end. of the tube. Such a tube is commonly referred to as being single ended. However, under these conditions, there is considerable capacity residing not only between the control grid and the anode of the tube but also between the leadingdn conductors of these electrodes and between their contact pins and socket terminals. because these elements parallel one another for .a considerable distance. Any one or all of these capacity effects may give rise to oscillations within the tube for well-known reasons, which prevents the tube from operating at its maximum translating efficiency.

An object of the present invention is to provide a single ended tube in which the capacity eifects between the control grid and the anode are eliminated or at least substantially reduced, and in addition, the capacity effects between the leading-in conductors, between the contact pins, between the contact terminals of the socket and between the conductors connected to said termine-ls are also reduced or preferably eliminated. In carrying out this object, I provide a metalenclosed tube in which the main body of the tube envelope is interposed between the contact pins respectively associated with the control grid and the anode of the tube in such a way as effectively to shield them from one another. Preferably the structure employed is such that the main portion of the tube is adapted to be received in a socket which is further provided with openings for receiving the contact pins of the tube.

The invention will be better understood when reference is made to the following description and the accompanying drawings in which Fig, 1 is a cross-sectional view taken along line l-l in Fig. 2 of a. tube and socket improved in accordance. with the present invention; Fig. 2 is a view taken along line 2-4. in Fig. 1; Fig. 3 is an elevational view partly in section of a modified type of tube and; socket provided with some of the improved shielding features of the present invention; Fig. 4 is a. view of the under side of the structure shown in Fig. 3; 5 is a crosssectlonal view taken, along line 5-5 in Fig. 4: Fig. 6 shows a modified form of the improved tube'and base, while Fig. 7 is a view of the under side of this structure;'Figs. 8 and 10 are still other forms of the improved tube, base, and socket structure and Fig. 9 is a view "of the under sideof these structures; Fig. 11 is aview taken along line |l--|l inF'ig. 10 and Fig.'l2 shows still another modification of the improved tube, base, and socket structure.

Referringmoreiparticularly toF-ig's. 1 and 2, numeral l designates acup-shaped envelope of metal which is drawn "downto a portion of smaller diameter in'dicated at 2, The'lower end of the" envelope is closed by an integral, flat plate 3, and the upper end-of'the envelope is provided with a'wide 'peripheralfia'nge'which is indicated at'4 and which 'pr'ovides an annular'surface directed toward the-closed end of the envelope. Ametal cap 5 is "positioned over the open end of the envelope I and is secured thereto in'any suitable manned-for "example, by butt-welding, to the flange '4. The envelope c'ontainsa cylindrical anode 6 an'd several grids including a secondary emission suppression grid 1, a screen grid 8, and a control grid 9. There is also an indirectly heated cathode l9 arranged within the control grid. The grids and the cathode are mounted in any suitable manner within the en.- velope and as shown, are arranged between two mica disks I Lone of which'is secured to the cap 5 and the other to a ring contained within the reduced diameter portion '2 of the envelope. A connection I3 is made to the anode 6 and this connection extends to a leading-in conductor M which is insulatingly taken through the envelope by any suitable form of seal, one of which will be described presently. A small strip 15 is cut out of the cap 5 and turned upward so as to leave a slot through which the connection I3 may extend. Connections for the various grids and the cathode are taken through a rectangular opening in the cap 5, the latter being provided with an upwardly extending lip 16. of clearness, only the connection. to the control grid has been illustrated in Fig. 1. This connection extends through a horizontal wire I! to a wire upright I8 which is taken through the envelope by means of a seal similar to that employed in connection withthe anode conductor. The seal for the control grid leading-in conductor is positioned preferably on the opposite side of the envelope I from the seal for the anode leadlng-in conductor. This is clearly shown in Fig. 2. These seals consist essentially of an eyelet I9 which is fitted in an opening in the flange 4 and is provided at the lower end with an outwardly For the sake extending flange for securing to the under side of the member 4. There are as many eyelets as there are leading-in conductors to be taken through the flange 4. The leading-in conductors are arranged at the center of the eyelet and insulated therefrom by means of a glass bead 20 as is well known in the art. The lower end of the leading-in conductors terminate in contact pins or prongs 2| which are supported by means of an insulating plate 24 and which may be of the tubular type soldered to the conductor or may be of the solid rod type butt-welded to the conductor. The various prongs are arranged in circular array and are all directed toward the closed end of the cup-shaped envelope part I.

There is provided about the seals a cupshaped metal cap 22 flanged at the bottom and welded or otherwise hermetically secured to the flanged plate 4. It will be noted that the combination of the cap 22 and the flange 4 forms a secondary enclosure which projects laterally beyond the contour of the envelope part I and which contains the various lead-in seals and their associated connections. An exhaust tubulation 23 (Fig. 2) may be secured to one side of the envelope I and after the envelope interior has been evacuated, the tubulation is collapsed and welded hermetically tight.

For making connections to the various contact pins, a socket is provided which may consist of a flat plate 24 of any suitable insulating material. This plate may be mounted by means of bolts which pass through openings 25 shown in Fig. 2. A slot or groove 26 is provided to receive the tubulation 23, thereby serving to locate the envelope l in the socket. Terminals are provided in the socket for the contact pins, these terminals consisting of small hollow metal cylinders 2'! which have earlike extensions 28 extending through openings in the plate 24. The interior diameter of the cylinders 21 is such as to cause a snug fit with the contact pins 2|. Wires may be connected to the ears 28 in order to energize the electrodes contained within the envelope.

When the tube is connected in a radio set, the envelope l is mounted on the chassis and is therefore maintained at ground or other fixed potential. Consequently, the envelope provides a region or partition of low or ground potential between the grid and anode contact pins, also between the anode and grid terminals in the socket. Moreover, the eyelets l9 and the metal caps and 22, which are all at the same potential as the envelope, provide a region of low or ground potential about and between the conductors I3 and I1. These grounded elements all add their shielding efiect to the extent that the anode leading-in conductor, contact pin, and socket terminal are electrostatically isolated from the corresponding elements of the control grid. There is therefore little or no tendency for deleterious capacity efiects to be set up either directly across the space or through the dielectric 24 between the anode and control grid or between any of the metal elements or conductors directly connected to them.

In Fig. 3 which shows another form of tube to which my inventiOn applies, numeral 30 designates a metal envelope closed at the top and flanged at the bottom to receive a metal header 3! which preferably is welded to the flange. The envelope contains a plurality of electrodes including a cathode, control grid, screen grid and anode of which only the leading-in conductors of the two grids and the anode have been illustrated in Fig. 3. These conductors are all taken through the same header by means of seals 32 similar to those shown and described in connection with Fig. 1. An evacuating tubulation 33 is also provided in the header. The leading-in conductors terminate in contact pins 34 which preferably are symmetrically arranged about the tube, and the contact pins for the control grid and the anode are arranged in approximately diametral positions, i. e., opposite from one another. This has been indicated in Fig. 4.

The socket for a tube of this character may consist of two plates 35 of insulating material which are bolted together and which carry between them the flanges of a number of contact terminals provided with ears 36. A spring clamp arrangement 31 of wellknown construction is secured to the under side of the lower plate 35 and is adapted to receive the evacuating tubulation 33 after the latter has been collapsed and welded to form a fiat extension. The clamping device 31 serves to locate the tube and the contact pins with respect to the socket and the contact terminals.

As pointed out hereinbefore, the contact pins of the control grid and anode are positioned on opposite sides of the tube and socket. In order electrostatically to shield these elements from one another, also to shield the socket terminals, I provide in accordance with the present invention a downwardly extending metal plate 38 which forms a wall or partition between the control grid and plate pins and terminals. The metal plate 38 preferably extends considerably below the contact pins and their socket terminals. The plate is provided with a horizontal portion 39 (Figs. 4 and 5) which can be riveted as indicated at 40 to the socket plates 35. The header 3| of the tube may be provided with an upwardly extending indented portion 4| as shown in Fig. 5 so as to clear the upper surface of the rivet 40. The socket may be connected to the chassis 42 of a radio set (Fig. 3) by means of the same bolts 43 which hold the two plates 35 together. In view of the fact that the grid and anode leading-in conductors and their contact pins and contact terminals are arranged on opposite sides of the socket and the plate 38 which is at a ground or fixed potential is positioned therebetween, the capacity effects, particularly the electrostatic lines which tend to pass through the dielectric 35 between the control grid and the anode are substantially eliminated.

Referring now to Figs. 6 and 7, there is shown a tube in which the shielding eflects are introduced by a metal lug which also serves to locate the tube in its socket. In these figures, numeral 45 designates the metal envelope of a tube which is closed at the bottom by a metal header having an annular inverted portion indicated at 46. The upper end (not shown) of the envelope 45 may contain a metal tubulation through which the envelope interior is evacuated. The envelope contains a plurality of electrodes of which only the leading-in conductors 41, 48 of the control grid and anode are illustrated. These conductors are taken through the inverted annular portion of the header by means of a glass seal indicated at 43 and terminate in contact pins 50 which are butt-welded to the leading-in conductors. These pins are rigidly held in position by means of a base 5| of insulatposite sides of the lug which fit openings in the base 5| so as all the more rigidly to secure the base to the tube. A socket (not shown) similar to those described in connection with Figs. 1 and 3 may be provided, the socket having an opening and keyway of the proper size to receive the locating lug 52 and the key 53. This lug is of suflicient length to extend beyond the contact pin 50 and also beyond the socket terminals (not shown) which receive the contact pins. It is apparent that when the tube is inserted into its socket, the envelope 45, the header 46 and the locating lug 52 are all at substantially ground potential, so that a region of low or fixed potential is provided between the contact pins 50, also between the corresponding contact terminals in the socket. Assuming that the active part of the control grid is shielded from the anode by means of a screen grid (not shown) the header 46 and the locating lug 52 complete the shielding by intercepting the electrostatic lines of force which tend to pass through or about the dielectric 5| between the leading-in conductors of the control grid and anode.

Figs. 8 and 9 show still another way of carrying my invention into effect. In Fig. 8, the reference character 56 designates a metal envelope closed at the top and terminating at the bottom in a flange 51. A header 58 of dished configuration is welded to the flange 51. This header is provided at the center with a metal evacuating tubulation 59. The envelope 56 contains a plurality of electrodes of which only the leading-in conductors 60 and BI respectively of the control grid and anode are illustrated. These conductors are taken through the header by means of eyelet seals 62 similar to those described in connection with Fig. l. A heavy plate 63 of insulating material closes the lower end of the header 58. Openings are provided in the base 63 to receive the hollow contact pins 64 which are secured at their lower ends by means of solder to their leading-in conductors. The base 63 is also provided with an opening 65 at the center in order to acommodate the tubulation 59. There is a downwardly extending hollow projection 66 of insulating material which forms part of the base 63 and is provided with a key 61.

The socket for a tube of this type is somewhat similar to that described in connection with the other figures except that there is a metal plate 68 which extends over the entire upper surface of one of the plates 68 and is secured to the latter by means of the bolts 10. Socket terminals ll are provided which receive the contact pins 64 and these terminals have extensions 12. As shown more clearly in Fig. 9., the plates 68 are provided with a central opening which receives not only the projection 66 but also the key 61 so that the latter serves to position the tube and the contact pins in the socket. As stated hereinbefore, the control grid leading-in conductor is positioned on the opposite side of the tube from the plate leading-in conductor as indicatedin Fig. 9. In order to shield the contact pins and socket terminals from one another, I provide on the socket a metal plate 13 which is bent so as to clear the various projecting members and which is positioned between the control grid and the plate socket terminals. This metal strip 13 can be secured in any suitable manner to the lower socket plate 69. This plate 13 is maintained at ground or other fixed potential by proper connection to the chassis of the radio set. It is apparent that the member 13 serves to intercept the electrostatic lines of force which tend to travel directly between the grid and anode socket terminals. The metal tubulation 59 is positioned between the control grid and anode leading-in conductors and therefore additionally serves to intercept these electrostatic lines of force. The metal plate 68 is maintained at ground or at other fixed potential, and this plate serves to intercept the electrostatic lines which tend to travel in curved paths through the insulating material and between the leading-in conductors, socket terminals, and contact pins. There is therefore provided an electrostatic shielding system which intercepts all the electrostatic lines of force which may pass through any of the paths between the grid and anode conductors and consequently, any deleterious electrostatic eifects in the tube are substantially eliminated.

In Fig. 10, I have disclosed a somewhat different form of shielding system which has particular application to glass tubes. Numeral I8 designates a glass envelope which contains an indirectly heated cathode 58, a control grid 80, a screen grid 8|, and an anode 82. Only the lead ing-in conductors of the control grid and anode are illustrated. As in the case of the other tubes previously described, the control grid conductor 83 and the anode conductor 84 are arranged at diametrically opposite positions where they pass through the lower end of the envelope I8. For shielding these conductors as they pass through the dielectric, I provide two metal disks 85 arranged on opposite sides of the base of the envelope, the upper disk being provided with an upwardly extending metal plate 85. These plates are electrically connected together and maintained at ground or other fixed potential. For evacuating the tube, I may provide a metal tubulation 81 which registers with an opening in the upper disk 85 passes through opening in the lower disk 85.

A base for a tube of this character may consist of a cup-shaped member of insulating material 88 which is secured at its upper end to reduced diameter portion of the envelope 1'8. This member is closed at the lower end and terminates in a downwardly extending projection 39 which is provided with a key 80. The leading-in conductors extend through the lower portion of the base 88 and connect with contact pins 95. These pins fit tightly in terminals 92 provided in the socket. As in the case of the tube shown 8, there is provided a horizontal metal plate 68 and a vertical metal plate 13. The construction of these plates and their purpose have been fully set forth in connection with 8 and 9. It is apparent that in addition to the shielding effects produced by these plates 58 and 13., I have provided additional shielding between. leading-in conductors by reason of the plates -85 and 86. The electrostatic lines of force which tend to flow through the glass base of the envelope between the leading-in conductors are attracted toward and intercepted by the upper and lower plate 85 and hence rendered innocuous. The metal tubulation 81 which also is at ground potential serves to intercept some of these electrostatic lines. The plate 88 would intercept those lines which tend to pass directly across the space between the grid and anode leading-in conductors.

The tube shown in Fig. 12 is somewhat similar to that described in connection with Fig. 10 except that a glass evacuating tubulation 95 is provided instead of a metal tubulation and the upper metal plate 85 carries a downwardly projecting metal extension 96. The lower metal plate 85 is also provided with a downwardly extending tubulation 97 which fits about the glass tubulation 95. After the envelope 18 has been evacuated, the glass tubulation 95 is sealed off by a torch. Instead of providing the metal plate 13 which is interposed between the control grid and anode socket terminals, as was explained in connection with Fig. 10, I provide in this modified tube a metal cylinder 98 around the projection 89 and key 90. This cylinder is provided with a flanged portion at the top as indicated at 99 which clamps about the two insulating plates 69 of the socket. The cylinder 98 extends downwardly beyond the contact pins 9! and their socket terminals 92. The metal members 85, 85, 96, and 98 are all maintained at ground or other fixed potential so that the electrostatic lines of force which tend to pass either through the dielectric or through the space between the control grid and anode leading-in conductors or their contact pins and terminals are intercepted and rendered innocuous. These metal members are also effectively interposed between conductors I connected to the socket terminals, assuming the conductors are brought out from opposite sides of the socket as indicated on the drawing. It is obvious that instead of employing a metal cylinder 93 surrounding the projection 89 to screen the socket terminals 92 and their contained pins 9! from one another, I may provide a plate member I3 similar to that shown in Figs. 8, 9 and 10. Indeed, any part of the projection 89 or the key 58 may be constituted of metal and grounded in order to serve adequately as an electrostatic shield, even in the absence of the metal cylinder 98. Many other alternative arrangements or combinations of the shielding structures described hereinbefore will suggest themselves to those skilled in the art in the light of the disclosure for providing a region or partition of low fixed potential between the input and output electrodes, their connections and socket terminals.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An electric discharge device comprising a cup-shaped part having a discharge space within it, electrodes within the said space, means sup porting a series of contact prongs in a circular array outside the periphery of said cup-shaped part with the prongs directed toward the closed end of said part, whereby certain of the prongs are separated from one another by the body of the part, and means connecting the respective contact prongs to the various electrodes within the discharge space.

2. An electric discharge device comprising a cup-shaped metal part having a discharge space within it, electrodes including a grid and an anode within the said space, means supporting a series of contact prongs in a circular array outside the periphery of said cup-shaped part so that the prongs are directed toward the closed end of said part, and means for connecting said grid and anode respectively to ones of said contact prongs which are on opposite sides of said cup-shaped part.

3. A vacuum discharge device comprising a cup-shaped part having a discharge space within it, electrodes within the said space, a hollow enclosure adjoined to the open end of the said cupshaped part, the marginal portion of said enclosure projecting laterally beyond the contour of the cup-shaped part so as to provide an annular flange surrounding said part and facing toward the closed end of the part, and terminals for the various electrodes sealed through said annular flang and terminating externally in contact prongs.

4. A vacuum discharge device comprising a flanged cup-shaped metal part having a discharge space within it, a cathode, a grid and an anode arranged concentrically within said cupshaped part and having terminal accessible at the open end of said part, lead-in wires for said electrodes sealed through the flange of said cupshaped part at spaced points around the part and connecting with said terminals, said lead-in wires terminating externally in contact prongs which project toward the closed end of said cup-shaped part, and a second cup-shaped part of greater diameter than the first part and hermetically joined to the flange of said first part in opposed abutting relation, whereby said second part encloses the inner extremities of said lead-in wires and their associated connections.

5. A discharge device comprising a cup-shaped metal part having a discharge space within it, electrodes including an anode, a cathode and a grid within said space, a hollow enclosure adjoined to the open end of the cup-shaped part, the marginal portion of said enclosure projecting laterally beyond the contour of the cup-shaped part so as to provide an annular flange surrounding the part and having its external surface directed toward the closed end of the part, externally accessible terminals for said enclosed electrodes mounted on said flange and distributed symmetrically around the periphery of the envelope, and means within the envelope for con necting said grid to a first one of said terminals and for connecting said anode to a second one of said terminals which is separated from said first terminal by the body of the cup-shaped part, whereby said anode and grid terminals are effectively electrostatically shielded from one another.

6. A discharge device comprising an envelope in the form of a flanged metal cup having a discharge space therein, an anode, a cathode and a grid enclosed within the said cup, a second metal cup of greater internal diameter than the first position in opposed abutting relation to the first cup to complete the enclosure of the discharge space, terminals insulatingly sealed through the flange on said first cup and extending into the space enclosed by the second cup, said terminals being formed externally as contact prongs positioned symmetrically around the periphery of the said first cup and extending toward the closed end thereof, and means for respectively connecting said anode and grid to selected ones of said terminals which are separated from one another by the body of said first cup.

JAMES E. BEGGS. 

